The project is focused on the elucidation of intracellular signal transduction pathways relevant to immune activation. A better molecular understanding of such pathways and their component parts will provide the foundation for identifying molecular defects which underlie various immunologic diseases, and it will also provide potential new targets for therapeutic interventions aimed at controlling destructive inflammatory reactions. Specifically, we wish to delineate signal-transducing events within immunologically relevant cells in response to pathogens, stress and/or mitogens. A central response to immunologic challenges is the production of cytokines belonging to the tumor necrosis factor (TNF) family, which in turn control many aspects of the final immune response by signaling through TNF receptors present on many cells. A primary target of TNF within cells is the transcription factor NF-kB, which induces expression of many genes with functions critical to controlling pathogens; this transcription factor is also essential for expression of HIV. We have identified a protein which represents a novel intracellular link in the relay of the signals which emanate from the cell surface after stimulation by TNF cytokines. Previously we have identified components involved in targeting NF-kB after stimulation through the T-cell receptor (TCR), which include the RAF kinase, best known for its activation of the cell growth-associated ERK MAP kinase. Ultimately we intend to help define the entire chain of events by which antigen stimulation, inflammatory cytokines and other immunologically important ligands may activate NF-kB. MAP kinase pathways are central to cellular differentiation, proliferation and stress responses. We have previously cloned a kinase (MEKK3) which functions within MAP kinase pathways. We have developed an inducible system which allows us to study the biologic effects of turning on only this kinase in cells. We have discovered a dramatic inhibitory effect of this kinase on cell cycle progression, suggesting that MEKK3 may function in cell cycle checkpoint controls.